This invention relates to a battery protection device for the protection of batteries and associated electric equipment from excess current or heat from the battery and to a method for making the device.
A battery protection device or battery protector (hereafter called battery protector) is electrically connected between a battery and its related electronic equipment such as a portable computer, a camera, communications instrument, automobile control equipment, and the like so that it can open the electrical circuit to the electronic equipment in the event that excess current or excess heat is received from the battery, thereby protecting the electronic equipment. Ordinarily, the battery protector is loaded in a casing accommodating secondary cells as the battery (hereafter called battery pack).
Along with the trend in recent years for reducing the size of electronic equipment, there has been a corresponding demand for efficiently locating the battery protector in a limited space within the battery pack. One of the effective ways of arranging the battery protector is one in which it is placed within one of the elongated openings formed between contiguous cylindrically-shaped secondary batteries. An elongated generally triangular gap is produced between contiguous batteries and the external wall of the battery pack and the battery protector having a cylindrical shape can be accommodated therein. A conventional battery protector comprises a pair of external terminals inserted into a tubular casing body with one end open and with the opening sealed tightly by an adhesive material with the pair of external terminals extending out of the sealed end thereof. Mounting a conventional battery protector in a gap inside the battery pack, typically includes the following problems: (a) Where one of the external terminals of the battery protector is to be connected to one end of a second cell, and the other external terminal is to be connected to the other end of another secondary cell, one of the external terminals of the protector must be bent toward the opposite end since both of the external terminals extend outwardly from the same end of the casing body. As a result, extra steps are required in connection with the accommodation of the battery protector and, at the same time, the efficient use of the space is compromised because of the bending. In addition, there tends to develop a dimensional error with regard to the connection to the secondary cells and the increased likelihood of the insulation film of the terminal being damaged by the edge of the bent part (b). In the battery protection made according to the prior art, moreover, due to the use of adhesive material for the sealing of the functional parts, there is a delay in the assembly process of placing the protector into the battery pack in order to allow for the completion of the hardening or curing of the adhesive agent (which is normally up to eight hours), thereby consuming a considerable time before the protector can be mounted.
Accordingly, an object of the present invention is the provision of a battery protector having an improved construction which overcomes the limitations and problems of the above noted prior art and effectively accommodates the protector in a battery pack and a method for making the battery protector. Another object of the invention is to provide improved efficiency for the preparation of a battery protector and thus improving productivity.
Briefly stated, a battery protection device made according to the invention comprises a hollow casing body which is formed by attaching a first casing member to a second casing member, a first end surface and a second end surface on the opposite side, a first external terminal that is caused to extend from the end of the first end surface, a second external terminal that extends from the second end surface, a first electrical contact arranged inside of the casing body and electrically connected to the first external terminal, a second electrical contact arranged inside of the casing body and electrically connected to the second external terminal and a thermostatic member such as a bimetal element connected to the first external terminal and, at the same time, mounting the first contact as a movable contact, thereby enabling opening and closing movement between the first contact and the second contact.
In view of the fact that the battery protection device made in accordance with the invention has external terminals disposed at opposite end surfaces, there is no need to use the device by bending one of the external terminals when used in the manner described above. In additional, the battery protection device made according to the invention does not use an adhesive agent in its assembly and this contributes toward an improvement in productivity.
According to a feature of the invention, at least one of the first and second terminals is insert-molded in at least one of the casing members. In one preferred embodiment, the first and second external terminals are made integral with and insert molded in the second casing member. According to another feature of the invention, a positive temperature coefficient of resistivity thermistor is connected in parallel with the bimetal element between the first and second external terminals. According a feature of a modified embodiment, one of the first and second casing members comprises an insulating film. The invention further comprises a battery pack in which the battery protection device is arranged in one of the gaps created between contiguous ones of a plurality of parallely disposed cylindrical batteries. In this arrangement, it is preferred that the battery protection device be serially connected in the electric current path that connects the plurality of batteries with the first and second external terminals being so arranged that the first external terminal and the second external terminals extend in different directions inside of a gap between contiguous batteries. The invention further comprises, in combination, electronic equipment that is equipped with the battery pack. The invention further comprises a method for making the battery protection device having a first casing member and a second casing member that form a hollow casing body with a first end surface and an opposed second end surface on the opposite side, comprising a step for insert molding of the second casing member with the first external terminal extending from the first end surface and, at the same time, the second external terminal extending from the opposite second end surface, a step for incorporating the first and second contacts and the bimetal element that relatively opens or closes the first and second contacts in the second casing member, and a step for ultrasonic wave welding of the first and second casing members on their engagement surfaces, thereby forming the hollow casing member. The method may further include a step for arranging the battery protection device in one of the gaps between contiguous batteries of a plurality of batteries that have been parallely arranged in a battery pack.
Additional objects and features of the invention will be set forth in the description which follows and in part will be obvious from the description. The objects and advantages of the invention may be realized and attained by means of the instrumentalities, combinations and methods particularly pointed out in the appended claims.